Governmental bodies continue to call for a reduction in the nitrogen oxides (NOx) and particulate matter (PM) emitted from diesel combustion processes, and in particular from diesel compression engines. While diesel particulate filters (DPF) are capable of achieving the required reductions in PM, which is typically a form of soot, there is a continuing need for improved systems that can provide the required reductions in NOx, often in connection with the PM reduction provided by a DPF.
Systems have been proposed to provide a diesel oxidation catalyst (DOC) upstream from a DPF in order to provide an increased level of NO2 in the exhaust which reacts with the soot gathered in the DPF to produce a desired regeneration of the DPF. This method may be referred to as passive regeneration. However, such systems may have limited effectiveness at temperatures below 300° C. and typically produce a pressure drop across the oxidation catalyst that must be accounted for in the design of the rest of the system. Additionally, or alternatively, fuel, such as hydrogen or a hydrocarbon fuel, can be delivered upstream of the DOC to generate temperatures greater than 600° F. and actively regenerate the DPF.
Some systems include a burner to ignite and combust unburned fuel that remains in the exhaust downstream from the diesel combustion process. Examples of such proposals are shown in commonly assigned U.S. patent application Ser. No. 12/430,194, filed Apr. 27, 2009, entitled “Diesel Aftertreatment System” by Adam J. Kotrba et al., the entire disclosure of which is incorporated herein by reference.
While current burners for such systems may by suitable for their intended purpose, improvements may be desirable. For example, it may be advantageous to provide a burner having an exhaust gas inlet coaxially aligned with the exhaust gas outlet to reduce back pressure and alleviate component packaging and mounting concerns.